<template>
  <div class="spec-preview" @mousemove="mouseMove">
    <img v-show="imgUrl" :src="imgUrl" />
    <div class="event"></div>
    <div class="big">
      <img v-show="imgUrl" :src="imgUrl" ref="bigImg" />
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
export default {
  name: "Zoom",
  props: ["skuDefaultImg"],
  data () {
    return {
      imgUrl: ""
    }
  },
  mounted () {
    //初始绑定一个自定义事件，用来接收imageList组件的传递的图片地址
    /* 
      给$bus绑定自定义事件,需要使用箭头函数作为回调函数,因为普通函数的this指向vue实例
    */
    this.$bus.$on("getDetailImg", (imgUrl) => {
      this.imgUrl = imgUrl
    })
  },
  methods: {
    mouseMove (e) {
      const oBigImg = this.$refs.bigImg
      const oMask = this.$refs.mask
      //鼠标到容器边缘的距离
      const mouseToBox = {
        x: e.offsetX,
        y: e.offsetY,
      }
      //获取mask元素的一半的宽高
      const maskWH = {
        x: oMask.offsetWidth / 2,
        y: oMask.offsetHeight / 2
      }
      //mask移动的距离
      const maskMove = {
        x: mouseToBox.x - maskWH.x,
        y: mouseToBox.y - maskWH.y,
      }
      //判断临界值
      if (maskMove.x < 0) {
        maskMove.x = 0
      } else if (maskMove.x > e.target.clientWidth - oMask.offsetWidth) {
        maskMove.x = e.target.clientWidth - oMask.offsetWidth
      }
      if (maskMove.y < 0) {
        maskMove.y = 0
      } else if (maskMove.y > e.target.clientHeight - oMask.offsetHeight) {
        maskMove.y = e.target.clientHeight - oMask.offsetHeight
      }
      //赋值
      oMask.style.left = maskMove.x + "px"
      oMask.style.top = maskMove.y + "px"

      //控制大图的移动
      oBigImg.style.left = -maskMove.x * 2 + "px"
      oBigImg.style.top = -maskMove.y * 2 + "px"
    }
  },
  watch: {
    //监听父组件传递过来的默认大图，当父组件请求数据成功后并通过props传递过来的时候，第一时间将图片赋值给初始值
    skuDefaultImg (newImg) {
      this.imgUrl = newImg
    }
  }
}
</script>

<style lang="less">
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover~.mask,
  .event:hover~.big {
    display: block;
  }
}
</style>